A composite material is a combination of at least two or more different active substances, which have distinctly different physical or chemical properties. The composite material created from them combines the physical and/or chemical properties of its constituent parts. At the same time, the positive properties for the respective application are brought to the fore and the least desired property is suppressed. The components are in this case chosen and combined with one another in such a way as to exploit the specific properties of each substance that are required for the case in question.
Fibre-plastic composites are distinguished by great potential for lightweight construction and are therefore used for making products that are subjected to high loading. However, their outstanding weight-to-strength ratio may only be fully utilized if all the phases of the process development and product development are performed appropriately for fibre plastics. Because of their short processing cycle times in the thermoforming process, thermoplastic fibre-plastic composites are especially used today in many application areas. The thermoforming of continuously fibre-reinforced thermoplastic semifinished products, known as organometallic sheets, offers great potential as a shaping process. To reduce the number of steps in the process, the thermoforming is also carried out in the injection mould. However, this reduces the possible complexity of the organometallic sheet used as a blank. Apart from the advantages mentioned, the clever combination of the thermoforming of organometallic sheets with the injection-moulding process also allows the costs for producing complex components to be reduced.
Organometallic sheets include special fabrics that are embedded in defined orientations in a thermoplastic matrix. The fabrics are produced from glass fibres, Kevlar fibres or carbon fibres. Polyamide is suitable, for example, as the thermoplastic matrix, for one reason because it exhibits good adhesion to the fibres. This results in hybrid components that consist entirely of plastic. In comparison with components of sheet metal, they are lighter and display greater surface stiffness and much higher strengths. Apart from the classic hybrid components, the application potential applies especially to components that must have great surface stiffness, such as, for example, spare wheel recesses. Moreover, add-on parts such as reinforcements or clips may be integrated by being moulded on.
It is also possible to dispense with corrosion protection, which represents an additional cost factor in the case of metallic sheet. A mould for thermoforming organometallic sheets is much less expensive than a tool for deep drawing metal. It is therefore especially worthwhile producing hybrid components from organometallic sheet in the case of low to moderate numbers of such components.
For the production of components it may be necessary to provide clearances, for example, in the form of passages or openings, which have to be introduced into the organometallic sheet. If these clearances are introduced into the organometallic sheet after the thermoforming, in the cooled-down state, for example by drilling or punching of the organometallic sheet, the structure of the reinforcing fibres is destroyed at the location of the clearance, which may lead to a weakening of the material at the clearance and around the clearance.
German Patent Publication No. DE 102010001634 A1 discloses a method in which a mandrel widens the fabric of the matrix while the matrix is still soft and able to be shaped in the thermoforming process. By introducing the mandrel, the material is prematurely fixed and, if there are a number of apertures, wrinkling may occur, since the flow of the material may not adjust appropriately. It is also known to heat the matrix once again locally after the thermoforming and to introduce a mandrel at this place. However, this involves additional effort and leads to problems when producing a number of apertures.